The invention relates to a valve arrangement for supplying air to an internal combustion engine. The invention further relates to a valve guide for such a valve arrangement.
In connection with combustion engines, turbo chargers are often utilized which comprise a turbine which is driven by the flow of exhaust gases. The energy which is thus absorbed by the turbine is then transferred via a shaft to a compressor which is arranged to compress the air on the intake side of the combustion engine and thus increase the amount of air in the combustion chamber. This means that a larger amount of fuel can be fed to a combustion chamber in an engine, thus increasing the torque and power of the engine.
In turbocharged diesel engines intended for, for example, commercial vehicles the available torque from the engine during take-off is often somewhat inadequate. The reason for this is that an engine equipped with a turbocharger performs worse than a normally aspirated engine at low rpm's due to that the turbo charger is a hindrance of the aspiration. The fact that the engine has a take-off performance which is worse than a normally aspirated engine means that the amount of air which is typical for a turbocharged diesel engine is not supplied. This in turn means that the amount of fuel which is injected in the engine must be limited at low rpm's, in order to minimize the amount of smoke from incomplete combustion due to lack of air. The turbo charger will with increased exhaust energy supply an additional amount of air which will permit an increased amount of fuel and by that increased engine torque and engine power.
The above-mentioned sequence of events is furthermore unfavorable since it contributes to reduced performance during the take-off phase of the engine. The engine will furthermore be perceived by users as “insufficient” during the take-off phase, since it has been necessary to limit the amount of fuel supplied during the initial “aspirating engine” phase, also known as turbo-lag.
One way of eliminating the above mentioned turbo lag, is to feed extra additional air and by that additional fuel, to the engine during this take-off phase or other load cases where engine response is required, in order to increase the engine response and by that increase the exhaust energy the turbo turbine which create the possibility of feeding extra air and fuel to the engine
For example, U.S. Pat. No. 6,138,616 discloses a valve arrangement in a combustion engine which is preferably equipped with a turbo unit, where the turbo function can be initiated earlier than in previously known devices and which adds to the starting torque of the engine. In particular, the valve arrangement comprises a secondary valve to supply additional air to the cylinder after the ordinary air supply from a main valve.
However, even though the disclosed apparatus provides a great improvement over prior art engines, there is still further room for improvement of the apparatus described in U.S. Pat. No. 6,138,616. The valve arrangement comprises a valve guide with a two piece design including an upper valve guide portion and a lower valve guide portion. A cavity is defined between the upper valve guide portion and the lower valve guide portion. This cavity is pressurized with compressed air when additional air is supplied via the secondary valve. This two-piece design of the valve guide require assembly with two different assembly tools in two separate operations followed by a reaming operation to secure a coaxial relationship between a centre axis of the upper valve guide portion and a centre axis of the lower valve guide portion.
It is desirable to provide a valve arrangement creating conditions for a more efficient assembly of the valve arrangement.
According to an aspect of the invention, a valve arrangement is provided for supplying air to an internal combustion engine, the valve arrangement comprising: a first valve for controlling an air supply to a cylinder, the first valve being movable between a closed position in which the air cannot be supplied to the cylinder and an open position in which the air is supplied to the cylinder, the first valve comprising: a first valve head, and a first valve stem comprising an inlet in a side wall of the valve stem, wherein the inlet is configured to receive additional air from a feeder channel, the first valve stem further comprising an internal passage, arranged in the length direction of the valve stem and fluidly connected to the inlet and configured to supply the additional air to the cylinder; a second valve arranged within the first valve and configured to control the flow of additional air to the cylinder, the second valve comprising a second valve stem and a second valve head contacting an inner surface of the first valve head when the second valve is in a closed position; a tubular valve guide arranged to surround a portion of the first valve stem such that the first valve stem is movable in the valve guide; characterized in that the valve guide comprises an inner groove forming a cavity between the valve guide and the first valve stem, wherein the valve guide further comprises a valve guide aperture configured to fluidly connect the inner groove to the feeder channel, and wherein the inlet of the first valve stem is aligned with the valve guide aperture when the first valve is in a closed position.
The definition that the valve guide is tubular should be interpreted to mean that the valve guide comprises an internal passage running along the length of the valve guide. Preferably, the internal passage has a substantially circular cross sectional shape. Moreover, the internal passage is adapted to match an outer dimension of the first valve stem such that the first valve stem is movable in the valve guide without there being any significant gap between the valve stem and the valve guide. Preferably, the first valve stem has a circular cross sectional shape defined by a diameter. The inlet of the first valve stem may also be referred to as a feeder hole, and the first valve stem may comprise one or more inlets, i.e. feeder holes. Moreover the first inlet valve may be regarded as the main or primary inlet valve, supplying the majority of air to the cylinder.
Designing the valve guide with the inner groove and the aperture forming a communication between a feeder channel in an engine head and the groove creates conditions for making the valve guide in a one-piece unit. This in turn creates conditions for a time-efficient assembly in that the valve guide may be positioned into its associated recess in the engine head via a single operation with a single assembly tool. Further, the valve guide design creates conditions for avoiding any additional machining after the positioning. Further, the valve guide design creates conditions for an accurate axial positioning of the groove relative to the feeder channel in the engine head on the outside and the inlet of the first valve stem on the inside. Further, such a one-piece valve guide design creates conditions for a cost-efficient production of the valve guide itself with proper tolerances.
According to one example, additional air is supplied to the cylinder from a compressed air tank when additional response is required from the engine, thus enabling an increased fuel amount to be supplied. This in turn generates a high increase in take-off performance, which eliminates the turbo-lag and the perception of the engine as being insufficient with regard to the take-off torque. In particular, turbo-lag may be overcome by means of the valve arrangement in a compensation system based on injection of pressurized air after main inlet valves are closing. The system comprises an electronic controller that controls the engine and the air injection system according to the following method steps: determining an engine operating condition including the boost pressure in the inlet manifold and in the extra accumulator air tank of compressed air in conjunction to the engine; determining if compressed air pressure is sufficient in the extra accumulator air pressure tank; determining an amount and/or duration of compressed air to be injected into the cylinder after the inlet valves are closed; determining a fuel amount adjustment based on the addition of pressurized air, desired air-fuel ratio, regulating/controlling the extra added air, after the inlet valves are closed, to a level near lambda 1 in air/fuel ratio and/or zero particulates is emitted in the engine out exhaust gases. It is determined to end the extra injection of air based on whether the turbo pressure is sufficient to take over the supply of requested air, or whether the torque demand of the driver has decreased.
According to an embodiment of the invention, the valve guide is made from a single piece. In particular, the valve guide can be machined from a single piece of material which is enabled by improved manufacturing methods. Thereby, the mechanical strength of the valve guide can be improved. Furthermore, the assembly process is simplified for a valve guide made from a single piece and no additional machining is required after the installation.
According to one embodiment of the invention, the inner groove is arranged to span the inner circumference of the valve guide. Thereby a cavity with a maximum volume is achieved for a given width of the groove, which in turn provides the largest possible addition of air to the cylinder via the one or more inlets in the first valve stem.
According to one embodiment of the invention, the inlet in first valve stem is arranged such that when the first valve is fully open, the inlet in the first valve stem is offset in relation to the valve guide aperture such that additional air is prevented from flowing from the feeder channel into the cylinder. Thus, when the first valve is fully open, no additional air can flow from the tank to the cylinder, and only the first valve, i.e. the main inlet, provides air to the cylinder. This minimizes the consumption of compressed air during an activation.
According to one embodiment of the invention, the second valve is configured such that the second valve head, when in an open position, does not protrude past an end face of the first valve head. Thereby, the valve arrangement can be used without having to adjust the valve recesses in the piston of the cylinder, since the second valve will not alter the outer geometry of the valve head of the first valve.
According to one embodiment of the invention, the valve arrangement further comprises a first spring connected to a first spring washer and a second spring connected to a second spring washer, wherein the first spring acts to close the first valve and the second spring acts to close the second valve. The first, outer, spring and washer are designed to provide the closing force to the internal second valve. The closing force thus contributes to the total closing force when the second valve is closed. The design means that the valve springs works independently when required and as an assembly when both valves are open.
According to one embodiment of the invention, a closing force of the second spring is higher than an air pressure force of additional air provided from said feeder channel. Thereby, additional air is prevented from flowing into the cylinder when the second valve is closed, even if the valve from the pressure tank is open so that additional pressurized air is provided to the valve arrangement.
According to one embodiment of the invention, the valve guide aperture is arranged so that a lower edge of the valve aperture does not reach below a lower edge of the groove. The location and diameter of the valve guide aperture is so located so that it does not affect the lower edge in the groove, which is important to achieve the correct timing of when the compressed air starts to be injected. The relative location of the lower edge of the groove versus the location and the size of the inlet of the first valve defines the timing and consumption of the air in the air injection.
There is also provided a vehicle or a stationary engine comprising a valve arrangement according to any one of the preceding embodiments.
According to an embodiment of the invention, there is provided an air supply arrangement for a combustion engine, the air supply arrangement comprising: a valve arrangement; a camshaft comprising a cam lobe, wherein the cam lobe is configured to control the first and second concentric valves such that the second valve opens prior to the opening of the first valve, and such that the second valve closes after the first valve has closed.
According to an embodiment of the invention the air supply arrangement further comprises a pressurized air tank for providing additional air a feeder channel fluidly connecting the air tank to the valve guide aperture; and a valve controlling the flow of air from the tank.
It is also desirable to provide a valve guide creating conditions for a more efficient assembly of a valve arrangement comprising the valve guide.
According to an aspect of the invention, a valve guide is provided for surrounding a portion of a first valve stem such that said first valve stem is movable in said valve guide, wherein the valve guide is tubular, characterized in that said valve guide comprises a recess in an inner surface for forming a cavity between said valve guide and said first valve stem, and that said valve guide further comprises an aperture fluidly connecting said recess with an outer surface of said valve guide.
More specifically, the valve guide is adapted so that the first valve stem may be moveably arranged in its main extension direction in the valve guide.
Designing the valve guide with the inner groove and the aperture for forming a communication between a feeder channel in an engine head with the groove creates conditions for making the valve guide in a one-piece unit. This in turn creates conditions for a time-efficient assembly in that the valve guide may be positioned into its associated recess in the engine head via a single operation with a single assembly tool. Further, the valve guide design creates conditions for avoiding any additional machining after the positioning. Further, the valve guide design creates conditions for an accurate axial positioning of the groove relative to the feeder channel in the engine head on the outside and the inlet of the first valve stem on the inside. Further, such a one-piece valve guide design creates conditions for a cost-efficient production of the valve guide itself with proper tolerances.
According to one embodiment, said valve guide is a one-piece unit. This creates conditions for a time-efficient assembly in that the valve guide may be positioned into its associated recess in the engine head via a single operation with a single assembly tool.
According to another embodiment, said recess forms a groove with a main extension in a circumferential direction of said valve guide. The groove creates conditions for a space-efficient structure for covering a plurality of circumferentially spaced inlets provided in the valve stem. According to one example, said recess forms a groove with a main extension in a direction perpendicular to an axial direction of said valve guide. According to a further example, said groove forms a continuous annular structure.
According to another embodiment, the recess is formed by machining the inner surface from an interior of the tubular valve guide. This creates conditions for a time-efficient production of the valve guide.
According to another embodiment, the aperture is positioned relative to the recess so that a surface defining the recess in an axial direction of the valve guide is at the same distance or closer to a first end of the valve guide than surface defining said aperture at the connection between the aperture and the recess. Thus, the aperture does not affect a lower edge of the recess defined by the surface defining the recess in the axial direction of the valve guide, which is adapted for controlling the timing of supply of the additional air to an associated cylinder.
According to another embodiment, the aperture is a hole with a circular cross section. It creates conditions for a time- and cost-efficient production, such as via drilling. According to one example, the aperture is therefore formed by a drilled hole.
According to another embodiment, an axis of the aperture is perpendicular to an axial direction of the valve guide.
According to another embodiment, said valve guide comprises a guide means adapted for guiding the valve guide to a circumferential position inside of a housing in which the aperture coincides with a feeder channel. According to one example, said guide means is positioned at a lower portion of the valve guide for engagement with an external tool during assembly.
According to another embodiment, a first portion of the valve guide comprising the aperture has a first diameter, and a second portion of the valve guide located adjacent to the first end of the valve guide has a second diameter smaller than the first diameter, thereby forming a tapered transition region between the first portion and the second portion of the valve guide, and wherein the guide means is located within the tapered transition region. Thereby, the external tool can use the tapered region as an identifier for where to locate the guide means.
According to another embodiment, the valve guide comprises a guide means in the form of a notch in the above described tapered region. The notch has a circumferential position aligned with a circumferential position of the aperture. Thereby, the assembly tool can utilize the notch as a guide means during to ensure that the aperture is correctly aligned in a valve arrangement comprising the valve guide. In other words, since the not is aligned with the aperture, the notch can be used to make sure that the aperture of the valve guide is aligned with an outlet of the feeder channel providing additional air to the cylinder via the valve arrangement.
According to another embodiment, the valve guide further comprises an alignment mark located between the aperture and a second end of the valve guide, wherein the alignment mark is configured to be visible when the valve guide is assembled in a valve arrangement. By observing the alignment mark of the valve guide after the valve guide has been arranged in the valve arrangement, it can be determined if the valve guide is located in the correct position such that the aperture is aligned with the feeder channel.
According to another embodiment, the alignment mark comprises a notch having a circumferential position aligned with a circumferential position of the aperture. A notch can be observed by means of a visual inspection, where it can be verified that the notch of the valve guide is aligned with a corresponding alignment mark of the valve arrangement in which the vale guide is mounted. However, the alignment mark of the valve guide may also be formed as an etch mark, an inscribed mark, or any other type of visually identifiable marking on the valve guide.
The invention further relates to a valve arrangement for supplying air to an internal combustion engine, the valve arrangement comprising: a first valve for controlling an air supply to a cylinder, the first valve comprising: a first valve head and a first valve stem; a valve guide according to any one of the alternatives above arranged to surround a portion of the first valve stem such that the first valve stem is movable in the valve guide.
According to another embodiment, the first valve stem comprising an inlet in a side wall of said valve stem, wherein said inlet is configured to receive additional air from a feeder channel via the aperture and the recess of the valve guide.
According to a further development of the last-mentioned embodiment, said first valve stem further comprising an internal passage arranged in the length direction of said valve stem and fluidly connected to said inlet and configured to supply said additional air to said cylinder.
According to a further development of the last-mentioned embodiment, the valve arrangement comprises a second valve arranged within said first valve and configured to control the flow of additional air to said cylinder, said second valve comprising a second valve stem and a second valve head.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.